The present invention relates to a polyimide-based composite formed using a precursor comprising a polyimide component and another polymer component, to electronic parts employing the polyimide-based composite and to a polyimide-based aqueous dispersion prepared by dispersing a precursor comprising a polyimide component and another polymer component in an aqueous medium.
1. Prior Art
Metal-clad laminates, which are prepared by impregnating a substrate such as glass fibers with a thermosetting resin solution and then laminating a prescribed number thereof which have been dried (prepregs), attaching copper foil or the like to one or both sides thereof and using heat contact bonding to harden the thermosetting resin, are used in printed wiring boards for industrial electronic instruments, OA devices, electrical appliances for public use, etc., and demand therefor has been increasing. In recent years, the trend toward smaller, lighter and more highly integrated electrical and electronic parts has accelerated efforts for greater stratification and higher density, and a strong demand has emerged for improvements in the adhesion, heat resistance and electrical properties of resin materials and the like used for such parts.
2. Problems to be Solved by the Invention
The most widely used thermosetting resins for electronic parts in the past have been epoxy resins which are mainly of the bisphenol A type. However, while such epoxy resins are superior in terms of the solubility of their uncured compositions in various solvents, their post-molding adhesion with metals such as copper foil and their chemical resistanc, heat resistance and electrical properties have been inadequate. In particular, the notable reduction in electrical properties after moist heat resistance testing has been an obstacle to their application for more highly integrated parts.
The use of polyimide resins has therefore been attempted in an effort to improve heat resistance.
Polyimide resins obtained by reaction between tetracarboxylic acid anhydrides and diamines have excellent electrical insulating properties, solvent resistance and mechanical properties and are used in many different fields including electric and electronic materials, aerospace technology, etc. However, in addition to problems such as poor solubility of their uncured forms in organic solvents making their impregnation into substrates difficult and the requirement for heat treatment at high temperature for curing reaction, they have generally been associated with other problems including low adhesion with various substrates, low water resistance and the tendency to cause deformation when coated onto metal thin films, because of the differences in thermal expansion coefficients.
On the other hand, with the recent downsizing and thickness and weight reduction of electrical products in recent years, there has been an increase in the use of flexible printed boards having metal foils attached to one or both sides of film-like resins, and metal-clad laminates (film laminates) for multilayer printed boards. There has also been an increased demand for electronic parts with resin layers formed using film-like resins. Currently, polyimide resins and polyester resins are primarily used as film-like resins. However, when a polyimide resin is used it is necessary to employ an adhesive at the interface with the copper foil, while polyester resins do not provide adequate heat resistance.
Moreover, increasing social awareness recently with regard to environmental safety in particular is creating a need to switch the media used from organic solvent systems to aqueous systems in the field of electronic materials as well. Yet, when it is attempted to supply a polyimide-based material with an aqueous medium the poor solubility of the polyimide in the aqueous medium makes it necessary to provide an aqueous dispersion form where the polyimide is dispersed in the aqueous medium. However, it has been very difficult to ensure sufficient storage stability for conventional polyimide-based aqueous dispersions.